1. Field of the Invention
The present invention is generally related to an engine cooling system and, more particularly, to a cooling system that provides a means for increasing the cooling of the engine block even when the cylinder head has not reached normal operating temperature.
2. Description of the Prior Art
Many types of engines, including internal combustion engines, are well known to those skilled in the art. Since the combustion process produces heat, some means must be provided to remove the heat from the areas of the engine block in which it could possibly cause distortion and damage. It is well known to provide cooling passages formed within the engine block. These cooling passages serve as conduits for the coolant, which is typically water. In marine applications, such as outboard motors, the coolant water is typically drawn from the body of water on which the outboard motor is being used and, after passing through the coolant path within the engine block, the water is discharged back into that body of water.
U.S. Pat. No. 5,295,881, which issued to Breckenseld et al on Mar. 22, 1994, discloses a marine propulsion device with coolant water passages. The device comprises an internal combustion engine including an engine block having therein a water jacket and having a lower face which includes therein a recess, a driveshaft housing connected to the lower face of the engine block, a propeller shaft rotatably supported by the drive shaft housing and adapted to support a propeller, a driveshaft extending through the driveshaft housing and including an upper end driven by the engine and a lower end drivingly connected to the propeller shaft, an exhaust housing located at least partially within the driveshaft housing and including an upper face mating with the lower face of the engine block and including therein a recess located in opposed relation to the recess in the lower face, a water passage defined by the recess in the lower face of the engine block and by the recess in the upper face of the exhaust housing, which has an inlet end and an outlet end spaced horizontally from the inlet end and communicating with the water jacket. It also comprises a conduit connected to the inlet end for supplying water to the inlet end.
U.S. Pat. No. 5,193,499, which issued to Binversie et al on Mar. 16, 1993, describes a cast inter-cylinder cooling passage for an internal combustion engine. The motor block for a multiple cylinder internal combustion engine, particularly an outboard motor, has a cooling passage that is integrally cast as a part of the motor block casting and extends from a water jacket in the cylinder head area to a water jacket space that is provided between the banks of cylinders in the v-block engine.
U.S. Pat. No. 4,559,908, which issued to Flaig et al on Dec. 24, 1985, describes a method for fabricating an integrally cast engine block including a plurality of cylinders, exhaust passage portions which respectively extend from the cylinders and which form portions of exhaust gas passages of equal length, and a water jacket cavity including portions in encircling relation to the exhaust passage portions. The method comprises the steps of providing a mold cavity which defines the exterior surface of the engine block, locating one or more disposable cores in the mold cavity so as to provide for the exhaust passage portions and for the water jacket cavity, filling the mold cavity with molten metal to provide a unitarily cast engine block, permitting solidification of the block with the cores contained therein, and removing the disposable cores from within the engine block to provide the hollow exhaust passage portions and the water jacket cavity.
U.S. Pat. No. 4,457,727, which issued to Flaig on Jul. 3, 1984, discloses a marine propulsion device engine cooling system. The device is provided with a flow of cooling water through the engine. The flow is controlled by a thermostat which controls the flow of cooling water in response to change in the temperature of the engine when the engine is operated at a low speed. The thermostat is supported in a flow restricting position when the engine speed is low, but is moved to a position providing for increased water flow when the engine reaches the increased speed.
U.S. Pat. No. 4,357,912, which issued to Brown on Nov. 9, 1982, discloses an engine cooling system for a marine propulsion device. The internal combustion engine has a water jacket with an inlet portion, a second portion, and a valve for communicating between the inlet portion and the second portion. It also comprises a valve member moveable relative to the valve port between open and closed positions, a recess extending from the inlet portion, a moveable wall connected to the valve member for actuation thereof between the open and closed positions wherein the movable wall has opposite first and second sides and extends across the recess to define a chamber located in the recess. It is subject to the pressure of the water in the inlet portion. The system also comprises a water pump driven by the engine which has a discharge outlet. A water supply conduit, which communicates with the discharge outlet and with the water jacket inlet includes an overboard discharge branch conduit communicating with the atmosphere. It also includes a duct communicating with the chamber and with the overboard discharge branch conduit. Furthermore, it comprises a valve in the overboard discharge branch conduit downstream of the connection with the duct and operable selectively to open and close the overboard discharge branch conduit relative to the atmosphere.
U.S. Pat. No. 3,908,579, which issued to Miller et al on Sep. 30, 1975, describes an outboard motor with a dual cooling system. The outboard motor includes a propulsion unit connected to a boat attachment element for providing vertical and horizontal swinging movement of the propulsion unit relative to the boat. The propulsion unit includes a rotary internal combustion engine including a first housing assembly comprising wall surfaces defining aligned first and second trochoid shaped rotor cavities and additional wall surfaces defining a first water jacket system adjacent to the first and second rotor cavities and having inlet and outlet ports. Together with a second housing assembly, it comprises wall surfaces defining aligned third and fourth trochoid shaped rotor cavities and additional wall surfaces defining a second water jacket system adjacent to the third and fourth rotor cavities and having inlet and outlet ports. Bolts secure together the first and second housing assemblies. The system further comprises a lower unit rigidly supporting the engine and including a propeller that is rotatably supported by the lower unit and operatably connected to the engine. A water pump, driven by the engine and having an inlet communicated with the water, is also provided along with a water conduit communicating between the pump and separately with each of the first and second water jacket system inlet ports.
All of the United States patents identified above by number are hereby expressly incorporated by reference in this description.
Many types of engine cooling systems utilize a thermostat and a pressure responsive valve to control the flow of coolant through the engine. The engine cooling system should ideally accomplish several goals. First, the cylinder block should be cooled sufficiently to prevent distortion or damage resulting from the extensive heat generated at the cylinder walls of the engine. Secondly, the cylinder head should be maintained at an efficient operating temperature. If the cylinder head is too cold, the operation of the engine is compromised. On the other hand, if the cylinder head is too hot, distortion and damage can occur. These problems can be exacerbated when the engine is operated on a cold body of water. Since water is typically drawn into the intake of the outboard motor from the body of water on which the motor is used, changes in the temperature of that water can adversely affect the operation of the engine. Typically, a thermostat is used to regulate the rate of flow of coolant through the cylinder head. A pressure responsive valve is used to regulate the flow of water through the cylinder block.
As an example of how an engine can respond inappropriately to its surrounding conditions, an outboard motor made according to the prior art being run at full speed on a cold lake could experience difficulty if the flow through both the cylinder block and cylinder head is controlled by the pressure responsive valve since the increased speed of the engine will open the valve regardless of the temperature. This could result in the cylinder head failing to reach appropriate operating temperatures. On the other hand, at low speeds when the pressure responsive valve remains closed, certain engine coolant schemes in the prior art control all of the water flow through the engine as a function of the thermostat. The cold lake water could retard the operation of the thermostat, which is most sensitive to the temperature of the water in the cylinder head, and result in an overheating condition in the cylinder block.
It would therefore be significantly beneficial if an engine cooling system could be developed which controls the rate of flow of coolant through the cylinder block as a function of engine speed, but also controls the rate of flow of coolant through the cylinder head as a function of temperature, regardless of the speed of operation of the engine.